Members

Each partition type that the EFI specification supports is identified by its own
GUID, which is published by the developer of the partition.

This member can be one of the following values.

Value

Meaning

PARTITION_BASIC_DATA_GUID

ebd0a0a2-b9e5-4433-87c0-68b6b72699c7

The data partition type that is created and recognized by Windows.

Only partitions of this type can be assigned drive letters, receive volume
GUID paths, host mounted folders (also called volume mount points), and be
enumerated by calls to FindFirstVolume and
FindNextVolume.

This value can be set only for basic disks, with one exception. If both
PARTITION_BASIC_DATA_GUID and
GPT_ATTRIBUTE_PLATFORM_REQUIRED are set for a partition on a basic disk that is
subsequently converted to a dynamic disk, the partition remains a basic partition, even though the rest of
the disk is a dynamic disk. This is because the partition is considered to be an OEM partition on a GPT
disk.

PARTITION_ENTRY_UNUSED_GUID

00000000-0000-0000-0000-000000000000

There is no partition.

This value can be set for basic and dynamic disks.

PARTITION_SYSTEM_GUID

c12a7328-f81f-11d2-ba4b-00a0c93ec93b

The partition is an EFI system partition.

This value can be set for basic and dynamic disks.

PARTITION_MSFT_RESERVED_GUID

e3c9e316-0b5c-4db8-817d-f92df00215ae

The partition is a Microsoft reserved partition.

This value can be set for basic and dynamic disks.

PARTITION_LDM_METADATA_GUID

5808c8aa-7e8f-42e0-85d2-e1e90434cfb3

The partition is a Logical Disk Manager (LDM) metadata partition on a dynamic disk.

This value can be set only for dynamic disks.

PARTITION_LDM_DATA_GUID

af9b60a0-1431-4f62-bc68-3311714a69ad

The partition is an LDM data partition on a dynamic disk.

This value can be set only for dynamic disks.

PARTITION_MSFT_RECOVERY_GUID

de94bba4-06d1-4d40-a16a-bfd50179d6ac

The partition is a Microsoft recovery partition.

This value can be set for basic and dynamic disks.

PartitionId

The GUID of the partition.

Attributes

The Extensible Firmware Interface (EFI) attributes of the partition.

This member can be one or more of the following values.

Value

Meaning

GPT_ATTRIBUTE_PLATFORM_REQUIRED

0x0000000000000001

If this attribute is set, the partition is required by a computer to function properly.

For example, this attribute must be set for OEM partitions. Note that if this attribute is set, you can use
the DiskPart.exe utility to perform
partition operations such as deleting the partition. However, because the partition is not a volume, you
cannot use the DiskPart.exe utility to
perform volume operations on the partition.

This attribute can be set for basic and dynamic disks. If it is set for a partition on a basic disk and the
disk is converted to a dynamic disk, the partition remains a basic partition, even though the rest of the
disk is a dynamic disk. This is because the partition is considered to be an OEM partition on a GPT disk.

GPT_BASIC_DATA_ATTRIBUTE_NO_DRIVE_LETTER

0x8000000000000000

If this attribute is set, the partition does not receive a drive letter by default when the disk is moved
to another computer or when the disk is seen for the first time by a computer.

This attribute is useful in storage area network (SAN) environments.

Despite its name, this attribute can be set for basic and dynamic disks.

GPT_BASIC_DATA_ATTRIBUTE_HIDDEN

0x4000000000000000

If this attribute is set, the partition is not detected by the Mount Manager.

As a result, the partition does not receive a drive letter, does not receive a volume
GUID path, does not host mounted folders (also called volume mount points), and
is not enumerated by calls to FindFirstVolume and
FindNextVolume. This ensures that applications
such as Disk Defragmenter do not access the partition. The Volume Shadow Copy Service (VSS) uses this
attribute.

Despite its name, this attribute can be set for basic and dynamic disks.

GPT_BASIC_DATA_ATTRIBUTE_SHADOW_COPY

0x2000000000000000

If this attribute is set, the partition is a shadow copy of another partition.

VSS uses this attribute. This attribute is an indication for file system filter driver-based software (such
as antivirus programs) to avoid attaching to the volume.

An application can use the attribute to differentiate a shadow copy volume from a production volume. An
application that does a fast recovery, for example, will break a shadow copy LUN and clear the read-only and
hidden attributes and this attribute. This attribute is set when the shadow copy is created and cleared when
the shadow copy is broken.

Despite its name, this attribute can be set for basic and dynamic disks.

Windows Server 2003: This attribute is not supported before Windows Server 2003 with SP1.

GPT_BASIC_DATA_ATTRIBUTE_READ_ONLY

0x1000000000000000

If this attribute is set, the partition is read-only.

Writes to the partition will fail.
IOCTL_DISK_IS_WRITABLE will fail with the
ERROR_WRITE_PROTECT Win32 error code, which causes the file system to mount as read
only, if a file system is present.

VSS uses this attribute.

Do not set this attribute for dynamic disks. Setting it can cause I/O errors and prevent the file system
from mounting properly.

Name

A wide-character string that describes the partition.

Remarks

The GPT partition format is required for disks that are used to boot computers that use
Extended Firmware Interface (EFI) firmware. GPT data disks can reside on x86, x64, and Itanium-based
architectures.

For more information about EFI, see
Firmware and Boot Environment. Starting with
Windows Server 2003 with SP1, GPT is supported on all Windows platforms, not only platforms that use
EFI.

See Also

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